Schistosoma mansoni, a human blood fluke parasite, causes a disease of major health importance in many parts of the world. During its life cycle, penetration of host tissues by this organism occurs at almost every stage. These penetration processes are, in some cases, likely to be mediated by lytic enzymes. In case of the cercarial stage, the role of proteolytic enzymes has been well documented. On histological grounds, schistosome eggs are also likely to penetrate host tissues utilizing proteases. Recently, we have described an acidic thiol-dependent protease in egg extracts, and plan to study its role in penetration. The penetration of the snail host by schistosome miracidium is also likely to be mediated by lytic enzymes. The aim of this project is to isolate, characterize, and compare the proteolytic enzymes in extracts and secretions of schistosoma mansoni eggs and miracidia. In addition, these enzymes will be compared with a related thiol protease from adult worms. The physical and enzymatic properties of the enzymes will be determined and their immunological cross-reactivity compared. The possibility will be tested that these enzymes may be related to antigens that elicit the host's immune response which is a principal cause of pathology of schistosomiasis.